Prior art devices have included several mechanisms wherein the rotary position of a door or the like has been actuated by a drive which drives the door to a position corresponding to the position to which an electric control element has been set. For instance, in the U.S. Pat. No. 4,616,164 to Kenny et al issued Oct. 7, 1986 there is disclosed a feedback servoactuator in which a motor drive drives a gear segment which mounts a wiper bridging across a conductive swipe and a resistive swipe disposed on a card adjacent the gear segment. Input of voltage determined by the position of the wiper is connected to a circuitry for a Wheatstone bridge. The Wheatstone bridge is also connected to a control voltage input determined by the setting of a potentiometer which is the command control element. The circuitry drives the actuator until a balance between the inputs is achieved.
Feedback servoactuators are employed in numerous applications where it is desired to rotate a shaft to a desired rotary position in response to an electrical command position signal. In the past such servoactuators have been used in vehicles to control the flapper door of an environmental air-conditioning system used to control the flow of heated or cooled air into the passenger compartment of a vehicle. Such applications require that the position of the door or vane be controlled in a range of, say 180.degree.. This has been accomplished by directly linking the shaft of the gear on which the wiper is mounted directly to the vane.
There is a need for an actuator in which the drive must be linked to a door drive element which has a travel of over 360.degree.. For instance, in some controls for ventilation in a vehicle, the valve may be in the form of a film which moves across a vent duct, the film having a window, the position of which registers more or less with the cross-section of the vent. The film itself may be spring-biased so that its end moves in one direction to valve off more or less air flow through the duct. In such arrangements, the film may be wound on a drum controlled by a drive motor. The drum may, in its travel moving the film, make more than one rotation. The control of rotation of the drum has to be such that the window or end of the film reaches a position as required by the temperature setting, for instance.
The present invention provides an servoactuator of the potentiometer feedback type in which the drive element arrives at the desired position in its numerous rotations as required by the command signal. This is accomplished in the present invention by the use of a planetary gear system which mounts a wiper on the ring gear, the wiper working against swipes of no greater than 360.degree..